1. Field of the Invention
This invention relates to an ultrasound imaging device. More particularly, this invention relates to an ultrasonic transducer for electronic focal scanning in an ultrasound imaging device. Still more particularly, this invention relates to a transducer which contains a number of piezoelectric elements which are arranged around a central axis and which are spaced from each other by grooves for decoupling purposes.
2. Description of the Prior Art
In the prior art (see, for instance, article "Annular Array Design and Logarithmic Processing For Ultrasonic Imaging" by H. E. Melton, Jr. and F. L. Thurstone in Ultrasound Med. Biol., Vol. 4, pp. 1-12), a transducer for electronic focal scanning is disclosed which contains an annular array of piezoelectric elements. Each of the piezoelectric rings is provided with electrodes in order to apply a voltage thereto in the emission mode and to derive a voltage therefrom in the receiving mode. The prior art annular array is provided with several grooves separating the individual rings from each other, thereby acoustically decoupling adjacent areas from each other.
For dynamic focusing in the B mode imager, for instance, such an annular transducer may be employed. The different annuli are switched in one after the other, and the transducer is focused at various positions along the imaging space. One of the problems associated with the prior art focal scanning device resides in the fact that annular arrays, particularly annular grooves are difficult to implement. Usually, a special sawing tool such as a core drill is necessary for each individual groove. Therefore, a variety of tools are required in the production of such a device. For any design change, again special tooling is needed. Furthermore, the individual grooves are relatively wide. This leads to a lack of sensitivity and will create grating lobes in the emission mode as well as in the receiving mode, which in turn will contribute to poor imaging performance. Additionally, wide grooves represent a waste of active area which could be used for emission and/or receiving. Finally, in the prior art design having annular elements, it is hard to produce very fine elements, that is elements of small thickness. In the prior art producing process, the tool is pressed against the surface of a piezoelectric ceramic applying pressure to the brittle plate. This presents a certain hazard of breaking. Fine elements are needed for high frequencies.